U.S. patent number 10,529,885 [Application Number 15/911,697] was granted by the patent office on 2020-01-07 for optical device and method for manufacturing the same.
This patent grant is currently assigned to Asahi Kasei Microdevices Corporation. The grantee listed for this patent is ASAHI KASEI MICRODEVICES CORPORATION. Invention is credited to Edson Gomes Camargo, Toshiaki Fukunaka.
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United States Patent |
10,529,885 |
Camargo , et al. |
January 7, 2020 |
Optical device and method for manufacturing the same
Abstract
PROBLEM TO BE SOLVED: To reduce an influence on an optical
device caused by stress variation on a resin sealing body due to an
environmental change and similar change. SOLUTION: An optical
device includes a substrate 11, a semiconductor lamination portion
formed on the substrate 11 and configured to receive or emit a
light, a protective layer 3 that has a shape to cover an entire
surface of the semiconductor lamination portion, a mold resin 6
configured to seal the protective layer 3 and the substrate 11
excluding a surface of the substrate 11 on an opposite side of a
surface on which the semiconductor lamination portion is formed.
The light is entered or emitted from a side of the substrate 11,
and the mold resin 6 includes a through hole 61 configured to pass
through from a top surface of the mold resin 6 to the protective
layer 3. A deformation of the mold resin 6 is reduced by the
protective layer 3 and the through hole 61. Then, stress variation
acting on an active portion 12 including the semiconductor
lamination portion can be reduced.
Inventors: |
Camargo; Edson Gomes (Tokyo,
JP), Fukunaka; Toshiaki (Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
ASAHI KASEI MICRODEVICES CORPORATION |
Tokyo |
N/A |
JP |
|
|
Assignee: |
Asahi Kasei Microdevices
Corporation (Tokyo, JP)
|
Family
ID: |
61629216 |
Appl.
No.: |
15/911,697 |
Filed: |
March 5, 2018 |
Prior Publication Data
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Document
Identifier |
Publication Date |
|
US 20180287005 A1 |
Oct 4, 2018 |
|
Foreign Application Priority Data
|
|
|
|
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Mar 31, 2017 [JP] |
|
|
2017-072210 |
Mar 31, 2017 [JP] |
|
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2017-072463 |
Nov 22, 2017 [JP] |
|
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2017-224702 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
31/0216 (20130101); H01L 27/15 (20130101); H01L
27/153 (20130101); H01L 33/52 (20130101); H01L
21/4803 (20130101); H01L 31/02366 (20130101); H01L
31/0203 (20130101); H01L 21/4846 (20130101); H01L
33/20 (20130101); H01L 31/12 (20130101); H01L
27/14 (20130101); H01L 33/62 (20130101); H01L
2933/005 (20130101); Y02E 10/50 (20130101) |
Current International
Class: |
H01L
21/56 (20060101); H01L 27/15 (20060101); H01L
27/14 (20060101); H01L 31/12 (20060101); H01L
31/0236 (20060101); H01L 21/48 (20060101); H01L
33/52 (20100101); H01L 33/20 (20100101); H01L
31/0216 (20140101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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S57-089273 |
|
Jun 1982 |
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JP |
|
H05-063068 |
|
Aug 1993 |
|
JP |
|
2001-127348 |
|
May 2001 |
|
JP |
|
2002-314142 |
|
Oct 2002 |
|
JP |
|
2002-324916 |
|
Nov 2002 |
|
JP |
|
2006-201226 |
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Aug 2006 |
|
JP |
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2006-294681 |
|
Oct 2006 |
|
JP |
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2006-324408 |
|
Nov 2006 |
|
JP |
|
2010-517289 |
|
May 2010 |
|
JP |
|
2011-205068 |
|
Oct 2011 |
|
JP |
|
2012-146826 |
|
Aug 2012 |
|
JP |
|
2013-201347 |
|
Oct 2013 |
|
JP |
|
2014078548 |
|
May 2014 |
|
JP |
|
2015-201657 |
|
Nov 2015 |
|
JP |
|
2016-092021 |
|
May 2016 |
|
JP |
|
6006602 |
|
Sep 2016 |
|
JP |
|
2016-189488 |
|
Nov 2016 |
|
JP |
|
2012/147608 |
|
Nov 2012 |
|
WO |
|
Other References
EPO translation of Sasayana, JP2014-78548, published May 1, 2014.
cited by examiner .
Decision to Grant a Patent dated Jan. 15, 2018 in counterpart
Japanese Patent Application No. 2017-224702. cited by
applicant.
|
Primary Examiner: Gumedzoe; Peniel M
Assistant Examiner: Johnson; Christopher A
Attorney, Agent or Firm: Morgan, Lewis & Bockius LLP
Claims
The invention claimed is:
1. An optical device, comprising: a substrate; a semiconductor
layer formed on the substrate, the semiconductor layer being
configured to receive or emit a light; a stress relaxation layer
having a shape to cover an entire surface of the semiconductor
layer; a resin sealing body configured to seal the stress
relaxation layer and the substrate excluding a surface of the
substrate on an opposite side of a surface on which the
semiconductor layer is formed; and a cavity formed between the
stress relaxation layer and the resin sealing body, wherein the
light enters or is emitted from a side of the substrate, wherein
the light passes through the substrate, wherein the resin sealing
body includes a through hole configured to pass through from a top
surface of the resin sealing body to the stress relaxation layer,
wherein the semiconductor layer includes a mesa structure portion,
and wherein a center of the cavity is formed above the mesa
structure portion.
2. The optical device according to claim 1, wherein the stress
relaxation layer includes a silicone resin.
3. The optical device according to claim 1, wherein the stress
relaxation layer includes a photosensitive resin.
4. The optical device according to claim 1, wherein the through
hole has a circular shape or a slit shape in top view.
5. The optical device according to claim 1, wherein the through
hole is disposed at a proximity of a center of the stress
relaxation layer in top view.
6. The optical device according to claim 1, wherein the stress
relaxation layer has Young's modulus equal to or less than 70
GPa.
7. The optical device according to claim 1, wherein the stress
relaxation layer has a thickness increased toward a center of the
substrate.
8. The optical device according to claim 1, wherein the stress
relaxation layer has a thickness of 1 .mu.m or more from an
uppermost surface of the mesa structure portion, and the cavity has
a thickness of 2 .mu.m or more.
9. The optical device according to claim 1, wherein the cavity is
formed in a whole region between the stress relaxation layer and
the resin sealing body.
10. The optical device according to claim 1, wherein a difference
between a linear expansion coefficient of a resin material forming
the stress relaxation layer and a linear expansion coefficient of a
resin material forming the resin sealing body is 50 ppm or more and
500 ppm or less.
Description
TECHNICAL FIELD
The present invention relates to an optical device, and more
specifically, relates to an optical device such as an optical
sensor or a light emitting device that has a sealing structure
sealed by a resin-molded package.
BACKGROUND ART
Recently, a light emitting element having a high luminous
efficiency and a photoelectric conversion element having a high
signal-noise ratio (SNR) have been developed to meet various needs.
These devices have been combined to develop an advanced sensor
module. For one example, there has been a gas sensor that employs a
non-dispersive infrared (NDIR) method. The conventional gas sensor
of the NDIR method has been used including a tungsten lamp as an
infrared light source and a thermopile as a light receiving
portion.
However, for achieving downsizing and low power consumption, a
configuration where a Light Emitting Diode (LED) is employed as a
light source and a quantum type infrared device is employed as a
light receiving portion has been becoming a future standard
structure of the gas sensor of the NDIR method. Higher sensitivity
and higher SNR of the light receiving portion and higher luminous
efficiency of a light emitting portion is achieved by using, for
example, a narrow gap compound semiconductor material in Groups
III-V as the light receiving portion and the light emitting
portion.
An optical device such as the quantum type infrared device and the
LED has been specifically attracting attention from a point of
achieving tremendous low power consumption of a gas sensor module.
These optical devices have another great feature that the optical
devices can be sealed by a resin mold. Sealing by the resin mold
ensures easily downsizing the light emitting portion and the light
receiving portion, and ensures improving respective performances of
the light emitting portion and the light receiving portion, that
is, enhancing the luminous efficiency of the LED and enhancing the
SNR of the light receiving portion achieve enhancing a resolution
and the SNR of the gas sensor that employs these optical
devices.
In addition to improve the performances of the light emitting
portion and the light receiving portion, future gas sensors using
NDIR method will require a long-term stability. In aspect of the
long-term stability, a signal drift caused by stress and heat is
apprehended.
That is, in a package (hereinafter also referred to as a
resin-molded package) where an optical device is molded by a
sealing resin, a stress variation caused by moisture absorption and
heat of the resin used for the mold possibly influences on a
variation of an amount of luminescence and a variation of light
receiving sensitivity of the optical device such as the infrared
device and the LED. Depending on the specification, especially, a
gas sensor that requests resolution for a ppb order causes a
significant error on a measurement result of gas concentration even
when an optical signal level slightly varies due to an influence of
a disturbance.
As a method for reducing the stress variation, there has been
proposed a method such that, for example, transmission means is
disposed on a region for receiving or emitting light on a
semiconductor chip and the other region is sealed with an
insulating resin that includes a filler, so as to match a thermal
expansion coefficient of a material of the semiconductor chip with
a thermal expansion coefficient of the resin, thus suppressing the
stress variation (for example, see PTL 1).
For example, PTL 2 discloses a method such that a protective film
is disposed to cover a substrate and an infrared light receiving
element mounted on the substrate, that is, a protective film for
protecting the infrared light receiving element is disposed between
the sealing resin of the package and the infrared light receiving
element, thus protecting the infrared light receiving element from
the stress of the sealing resin. PTL 2 also discloses a method such
that the protective film is disposed to protect the infrared light
receiving element for reducing the influence of the stress, and
furthermore, a cavity region is disposed between the protective
film and the sealing resin to improve photoelectric conversion
efficiency, thus ensuring the reduction of the influence of the
stress.
CITATION LIST
Patent Literature
PTL 1: JP 2011-205068 A
PTL 2: Japanese Patent No. 6006602
SUMMARY OF INVENTION
Technical Problem
However, as described above, in the method where the transmission
means is disposed on the region for receiving or emitting light and
the other region is sealed with the insulating resin that includes
the filler, on a portion where the transmission means is not
disposed, a stress is caused by moisture absorption and heat of the
resin similar to conventional method, thus possibly affecting a
variation of an amount of luminescence and a variation of light
receiving sensitivity of an optical device (a quantum type infrared
sensor, LED).
In the method where the cavity region is disposed between the
protective film and the sealing resin, the photoelectric conversion
efficiency is ensured to improve while the influence of the stress
on the element is not reduced. Therefore, a method for reducing the
stress itself that the element receives so as to reduce the
influence of the stress with more certainty has been desired.
The present invention has been made in view of the above-described
circumstances, and it is an object of the present invention to
provide an optical device and a method for manufacturing the
optical device that ensures reduction of an influence caused by the
occurrence of stress variation on a mold resin due to an
environmental change and the like while reducing stress itself that
an element receives and efficiently exchanging light between a
light emitting portion and a light receiving portion, and an
outside of the optical device.
Solution to Problem
To achieve the above-described object, an optical device according
to one embodiment of the present invention includes a substrate, a
semiconductor layer formed on the substrate and configured to
receive or emit a light, a stress relaxation layer having a shape
to cover an entire surface of the semiconductor layer, and a resin
sealing body configured to seal the stress relaxation layer and the
substrate excluding a surface of the substrate on an opposite side
of a surface on which the semiconductor layer is formed. The light
is entered or emitted from a side of the substrate. The resin
sealing body includes a through hole configured to pass through
from a top surface of the resin sealing body to the stress
relaxation layer.
A method for manufacturing an optical device according to another
embodiment of the present invention includes: fixing a
semiconductor chip between lead frames by die bonding, the
semiconductor chip being formed on a substrate, the semiconductor
chip including a semiconductor layer configured to receive or emit
a light; electrically connecting the lead frame to the
semiconductor chip by a wire; forming a stress relaxation layer on
a surface on which the semiconductor layer of the substrate is
formed; and sealing the stress relaxation layer and the substrate
excluding a surface of the substrate on an opposite side of the
surface on which the semiconductor layer is formed such that a
through hole is formed to cause a part of the stress relaxation
layer to be exposed, by filling a resin between the lead frames
after forming the stress relaxation layer.
Advantageous Effects of Invention
According to one aspect of the present invention, an influence of a
stress variation generated on a resin sealing body can be reduced,
and an optical device that ensures long-term stability can be
provided.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a cross-sectional view illustrating a schematic
configuration of an optical device according to a first embodiment
of the present invention;
FIG. 2 is a cross-sectional configuration diagram illustrating an
exemplary active portion;
FIG. 3 is a cross-sectional configuration diagram illustrating an
exemplary semiconductor lamination portion;
FIGS. 4A to 4D are exemplary cross-sectional views describing
manufacturing processes of the optical device according to the
first embodiment;
FIG. 5 is an explanatory drawing used for describing operations of
the optical device according to the first embodiment;
FIGS. 6A and 6B are explanatory drawings used for describing the
operations of the optical device according to the first
embodiment;
FIG. 7 is a cross-sectional view illustrating a schematic
configuration of an optical device according to a second
embodiment;
FIG. 8 is a cross-sectional view illustrating a schematic
configuration of an optical device according to a third
embodiment;
FIG. 9 is a cross-sectional configuration diagram illustrating an
exemplary detail of a main part of FIG. 8;
FIGS. 10A to 10E are cross-sectional process drawings describing an
exemplary method for manufacturing a cavity;
FIGS. 11A to 11E are cross-sectional process drawings describing
the other example of the method for manufacturing the cavity;
FIG. 12 is a cross-sectional view illustrating a schematic
configuration of a modification of the optical device according to
the third embodiment;
FIG. 13 is a cross-sectional view illustrating a schematic
configuration of a modification of the optical device according to
the third embodiment;
FIG. 14 is a cross-sectional view illustrating a schematic
configuration of a modification of the optical device according to
the third embodiment;
FIG. 15 is a cross-sectional view illustrating a schematic
configuration of an optical device according to a fourth
embodiment;
FIGS. 16A to 16D are exemplary cross-sectional views describing
manufacturing processes of the optical device according to the
fourth embodiment;
FIG. 17 is an explanatory drawing used for describing operations of
the optical device according to the fourth embodiment;
FIG. 18 is a cross-sectional view illustrating a schematic
configuration of an optical device according to a fifth
embodiment;
FIG. 19 is a cross-sectional view illustrating a schematic
configuration of an optical device according to a sixth
embodiment;
FIG. 20 is a cross-sectional configuration diagram illustrating an
exemplary detail of a main part of FIG. 19;
FIGS. 21A to 21E are cross-sectional process drawings describing an
exemplary method for manufacturing a cavity;
FIGS. 22A to 22E are cross-sectional process drawings describing
the other example of the method for manufacturing the cavity;
FIG. 23 is a cross-sectional view illustrating a schematic
configuration of a modification of the optical device according to
the sixth embodiment;
FIG. 24 is a cross-sectional view illustrating a schematic
configuration of a modification of the optical device according to
the sixth embodiment;
FIG. 25 is a cross-sectional view illustrating a schematic
configuration of a modification of the optical device according to
the sixth embodiment; and
FIG. 26 is a characteristic diagram illustrating a variation of an
internal resistance of the optical device according to the sixth
embodiment when a temperature and humidity environment is
varied.
DESCRIPTION OF EMBODIMENTS
The following detailed description describes many specific concrete
configurations for complete understanding of the embodiments of the
present invention. However, it is apparent that other embodiments
and aspects can be embodied without being limited to the specific
concrete configurations. The following embodiments do not limit the
invention according to the claims and include all the combinations
of the distinctive configurations described in the embodiments.
The following describes one embodiment of the present invention
with reference to the drawings. In the following description of the
drawings, like reference numerals designate identical elements.
However, the drawings are schematically illustrated, and relations
between thicknesses and planar dimensions, ratios of thicknesses of
respective layers, and the like are different from actual
values.
First, a first embodiment of the present invention will be
described.
FIG. 1 is a cross-sectional configuration diagram describing an
optical device according to the first embodiment of the present
invention. FIG. 1 illustrates a schematic configuration of an
optical device 1 according to the first embodiment.
The optical device 1 according to the first embodiment includes a
light receiving/emitting element 2 that has a photoelectric
conversion function, a protective layer (stress relaxation layer)
3, and a terminal portion 5 connected to the light
receiving/emitting element 2 by a wire 4 connected to a wire pad
(not illustrated) of the light receiving/emitting element 2. The
light receiving/emitting element 2 includes a substrate 11 and an
active portion 12 formed on the substrate 11. The protective layer
3 is continuously formed to cover the active portion 12 and to
cover at least a part of the substrate 11. The protective layer 3
is formed to have a thickness increasing toward the center of the
substrate 11. Between the terminal portion 5 and the light
receiving/emitting element 2, a mold resin (a resin sealing body) 6
is filled. The mold resin 6 includes a through hole 61 that extends
in a direction from a top surface of the mold resin 6 to the
protective layer 3 to pass through the mold resin 6.
The protective layer 3 only needs to be disposed to cover at least
an entire surface of the active portion 12, and is not necessarily
required to cover the substrate 11.
The following sequentially describes each component of the optical
device 1.
<Substrate>
The optical device 1 illustrated in FIG. 1 has an entrance and exit
of light on a surface on an opposite side of a surface where the
active portion 12 of the substrate 11 is formed. In this case,
preferably, the substrate 11 has a high transmittance, for example,
a transmittance equal to or more than 30% to a wavelength of an
emitted or a received light. Further, for enhancing a light
propagation efficiency between a semiconductor lamination portion
21 of the optical device 1 and the outside of the optical device 1,
the transmittance is preferably configured to be equal to or more
than 40% or 50%.
The substrate 11 is selected such that the semiconductor lamination
portion 21 is formed to have a lamination with a high quality. As a
specific example, a substrate made of Si, GaAs, sapphire, and
similar material may be applied to the substrate 11. As described
above, since the optical device 1 includes the substrate 11 as a
light extraction port or a light emission port, the substrate 11 is
required to have a high transmittance, for example, equal to or
more than 30% to the wavelength. For example, when the
semiconductor lamination portion 21 is made of a narrow-gap
semiconductor material (for example, AlInSb) that contains In, Sb,
As, and Al, the substrate 11 may be a semi-insulating GaAs. This is
preferable because crystalline growth is allowed with high quality
and a high transmittance to a light having the wavelength of a few
.mu.m is provided.
<Active Portion>
As illustrated in FIG. 2, the active portion 12 includes the
semiconductor lamination portion 21, an insulating layer 22, and a
wiring layer 23.
<Semiconductor Lamination Portion>
As illustrated in FIG. 3, the semiconductor lamination portion 21
includes a first conductivity-type semiconductor layer 311, a first
barrier layer 312, an active layer 313, a second barrier layer 314,
and a second conductivity-type semiconductor layer 315, and is
configured to emit or receive a light.
The active portion 12 disposed in the optical device 1 according to
one embodiment of the present invention is not limited to the
laminated structure described here, and the laminated structure
(including the material and the number of layers) is not
specifically limited insofar as the structure is configured to emit
or receive the light having the wavelength necessary for a use of a
gas sensor and the like.
As a specific example, a PIN structure that includes the first
conductivity-type semiconductor layer 311 as an n-type
semiconductor, the active layer 313 as an intrinsic semiconductor,
and the second conductivity-type semiconductor layer 315 as a
p-type semiconductor may be employed. In this case, for enhancing
the luminous efficiency, the first barrier layer 312 configured to
reduce hole diffusion to the first conductivity-type semiconductor
layer 311 and the second barrier layer 314 configured to reduce
electron diffusion to the second conductivity-type semiconductor
layer 315 may be disposed. The semiconductor lamination portion 21
is allowed to employ a known material that has sensitivity or a
light emitting function to infrared, and for example, a
semiconductor layer that contains InSb may be applied.
As illustrated in FIG. 3, the semiconductor lamination portion 21
has a two-step mesa structure. The two-step mesa structure can be
formed by photolithography and etching. As a method for etching,
wet etching and dry etching may be used.
<Insulating Layer>
A material that has insulation property and can reduce at least any
one of physical damage and chemical damage may be employed as the
insulating layer 22, and for example, SiO.sub.2, SiN, and a
laminated body of them may be employed.
<Wiring Layer>
The active portion 12 may include multiple PIN structures (that is,
the semiconductor lamination portions 21) that are connected to one
another. For example, as illustrated in FIG. 2, the multiple PIN
structures may be connected in series. In this case, the wiring
layer 23 has a role to ensure the electrical connection. The wiring
layer 23 is made of a conductive material that contains Au, Ti, Pt
and the like. The wiring layer 23 may have the laminated structure
formed of Au, Ti, Pt and the like.
<Protective Layer>
The optical device 1 according to one embodiment of the present
invention includes the protective layer 3 configured to cover the
light receiving/emitting element 2. The protective layer 3 is made
of a material that reduces stress variation caused by deformation
of the mold resin 6 due to deformation of the protective layer 3
when the mold resin 6 expands. As a material that has such
property, a material more flexible than the resin material
constituting the substrate 11 and the mold resin 6, that is, a
material having a low Young's modulus is preferable, and the
material may have the Young's modulus equal to or less than 70 GPa.
As the protective layer 3, silicone resin, photosensitive silicone
resin, PIMEL (photosensitive polyimide), epoxy, and similar
materials may be applied. The material of the protective layer 3 is
preferable as the Young's modulus is small, and preferably, the
Young's modulus is lower than at least the Young's modulus of the
substrate 11.
The protective layer 3 has a height of the surface from a top
surface of the substrate 11 as a reference such that, for example,
when a plurality of the semiconductor lamination portions 21 are
formed on the substrate 11 as illustrated in FIG. 1, the height is
preferably 0.5 .mu.m or more, further preferably 1 .mu.m or more on
a position of the semiconductor lamination portion 21 formed
closest to an outer periphery of the substrate 11, and the upper
limit value of the height is preferably approximately 200 .mu.m. On
a position of the semiconductor lamination portion 21 formed at a
proximity of the center of the substrate 11, the protective layer 3
has the height of the surface from the top surface of the substrate
11 as a reference configured corresponding to the height of the
surface of the protective layer 3 on the position of the
semiconductor lamination portion 21 formed closest to the outer
periphery of the substrate 11. That is, when the height of the
surface of the protective layer 3 from the top surface of the
substrate 11 as a reference on the position of the semiconductor
lamination portion 21 formed on the most edge portion is defined as
H, the height of the surface of the protective layer 3 on the
position of the semiconductor lamination portion 21 formed at a
proximity of the center of the substrate 11 is preferably
approximately equal to or more than 1.5.times.H .mu.m and equal to
or less than 100.times.H .mu.m.
<Terminal Portion>
The terminal portion 5 has an electrical connection function and a
role as a supporting portion in assembly. Therefore, the terminal
portion 5 is disposed to have an upper end portion and a lower end
portion exposed to top and bottom surfaces of the optical device 1,
respectively.
The electrical connection here means to electrically connect the
active portion 12 to an external circuit. For the electrical
connection inside the optical device 1, the wire 4 disposed by a
wire bonding process is used. The wire 4 is connected to the
terminal portion 5 and the wiring layer 23 (see FIG. 2) disposed on
the substrate 11 to function as a wire pad.
The terminal portion 5 has a stepped surface 5a formed by removing
a part of a side facing the light receiving/emitting element 2. The
wire 4 is connected to the stepped surface 5a of the terminal
portion 5. The stepped surface 5a is formed by half etching of the
terminal portion 5.
The terminal portion 5 has a thickness of, for example, 0.5 mm or
less.
The terminal portion 5 is made of a metallic material such as
copper (Cu) or a copper alloy, and iron (Fe) or an alloy containing
iron, and especially, preferred to be made of copper. On the
terminal portion 5, for example, a nickel (Ni)-palladium (Pd)-gold
(Au) plating may be applied over surfaces other than the outer
surfaces of the terminal portion 5 exposed from the mold resin 6.
The nickel (Ni)-palladium (Pd)-gold (Au) plating is a laminated
plating where a nickel (Ni) plating, a palladium (Pd) plating, and
a gold (Au) plating are formed in this order on a predetermined
surface of the terminal portion 5 made of copper (Cu) and similar
material. The nickel (Ni) plating contributes to improvement of
strength of the terminal portion 5, the palladium (Pd) plating
contributes to improvement of wire bonding property of the wire 4,
and the gold (Au) plating contributes to improvement of
solderability on mounting. On the terminal portion 5, an argentum
(Ag) plating may be applied over a surface where the wire 4 is
wire-bonded, and a tin (Sn) plating may be applied over a top
surface (amounting surface) of the terminal portion 5 exposed from
a top surface of the mold resin 6. The argentum (Ag) plating
contributes to the improvement of the wire bonding property of the
wire 4, and the tin (Sn) plating contributes to the improvement of
the solderability on mounting.
<Mold Resin>
The optical device 1 according to one embodiment of the present
invention includes the mold resin 6 that seals the light
receiving/emitting element 2 via the protective layer 3. The mold
resin 6 has a role to fix the substrate 11 and the terminal portion
5. In the optical device 1 according to one embodiment of the
present invention, the light receiving/emitting element 2 is sealed
by the mold resin 6 excluding the bottom surface. However, the mold
resin 6 only needs to be configured such that a desired light can
enter the semiconductor lamination portion 21 via the substrate 11,
and it is not specifically limited which surface of the light
receiving/emitting element 2 is covered. For example, the mold
resin 6 may cover a part of the bottom surface of the light
receiving/emitting element 2, and does not have to cover a part of
the side surface of the light receiving/emitting element 2.
From an aspect of mass-productivity and mechanical strength, the
mold resin 6 may be epoxy resin used for a common semiconductor
device. However, for reducing the influence of the stress due to
the moisture absorption of the optical device 1, a material having
a low water absorption rate is preferable.
Especially in the case of the optical device 1 that includes the
semiconductor lamination portion 21 formed of the narrow-gap
semiconductor, a leak current in the structure of the optical
device 1 varies due to even a slight stress, thus easily causing
variation in electric property. Therefore, for the mold resin 6, a
resin having a low stress due to the moisture absorption and the
temperature may be preferably selected.
The material constituting the mold resin 6 may include a filler,
inevitably mixed impurities, and similar material besides the resin
material such as the epoxy resin. A mixing amount of the filler is
preferably 50 volume % or more and 99 volume % or less, more
preferably 70 volume % or more and 99 volume % or less, and further
preferably 85 volume % or more and 99 volume % or less among the
materials constituting the mold resin 6.
The mold resin 6 has a thickness, that is, a length between the top
surface and the bottom surface of the mold resin 6 in FIG. 1 of
preferably 0.5 mm or less, for example.
The through hole 61 only needs to be a through hole extending
perpendicular to the substrate 11 or extending in a direction close
to perpendicular. Disposing the through hole 61 ensures the
reduction of the stress in a package due to a thermal history of
the optical device 1.
The through hole 61 may be disposed on any portion of the mold
resin 6 insofar as the through hole 61 penetrates to the protective
layer 3.
The through hole 61 is preferred to be disposed at a proximity of
the center of the protective layer 3 in top view because the stress
is efficiently reduced. For example, in a case of the optical
device 1 where a plurality of the semiconductor lamination portions
21 are arranged lengthwise and crosswise in a matrix, the through
hole 61 is disposed on the center of the protective layer 3 that
covers the entire surface of the active portion 12 including the
plurality of the semiconductor lamination portions 21.
A plurality of the through holes 61 may be disposed, and it is only
necessary that at least one through hole 61 is disposed.
The through hole 61 may be formed in any shape in top view, and may
be formed in, for example, a circular shape and a slit shape. The
through hole 61 that has the circular shape in top view is
preferable because the through hole 61 is easily formed with a high
aspect ratio such as "1:100". When it is necessary to prevent
invasion of dust and the like through the through hole 61 and
similar case, the through hole 61 is preferred to be formed in the
slit shape.
Next, a method for manufacturing the optical device 1 will be
described by referring to cross-sectional views illustrated in
FIGS. 4A to 4D.
First, a wafer dicing process is performed to individualize the
substrate 11 from a state of a wafer into chips of the light
receiving/emitting element 2 (hereinafter also referred to as
semiconductor chips 2).
Next, a plurality of the individualized semiconductor chips 2 are
fixed on an adhesive sheet 102 where lead frames 101, which are
formed as the terminal portions 5 later, are fixed, and the wire
bonding process is performed to electrically connect the
semiconductor chip 2 to the lead frame 101 (the terminal portion 5)
by the wire 4 (FIG. 4A). The adhesive sheet 102 may be
preliminarily included on the lead frame 101.
Next, a potting process is performed to form the protective layer 3
(FIG. 4B). That is, a resin for forming the protective layer 3 is
dropped on the substrate 11 so as to cover the entire surface of
the active portion 12 of the semiconductor chip 2. Then, a shape of
the dropped resin is held as it is to form the protective layer 3.
This forms the protective layer 3 having the thickness increased
toward the center of the substrate 11. In the resin potting
process, a dispenser device for liquid resin may be used.
Next, a transfer molding is performed by using an upper mold 111 to
form the mold resin (FIG. 4C).
The upper mold 111 includes protrusions 111a for forming the
through holes 61 on positions facing the centers of the substrates
11. On the upper mold 111, a sheet 112 is arranged so as to cover
the entire surface on a side where the protrusions 111a are formed.
The sheet 112 is made of Teflon (registered trademark), for
example. When the upper mold 111 including the protrusions 111a is
used to fill a molten resin to be formed as the mold resin 6, the
sheet 112 disposed on the upper mold 111 reduces the stress acting
on the optical device when the upper mold 111 contacts the optical
device. Then, damages on the optical device due to the upper mold
111 are reduced and a frequency of defective products is lowered,
thus providing the effects of quality improvement and
mass-productivity improvement of the optical device.
The upper mold 111, on which the sheet 112 is disposed, is
positioned to contact the lead frame 101 (the terminal portion 5)
so as to face a lower mold 103, and the molten resin is filled
between the sheet 112 and the adhesive sheet 102 from a side.
Before the process performing the transfer molding, a process to
cure the protective layer 3 may be provided. Filling the molten
resin forms the through hole 61 that passes through the mold resin
6 on the center of the substrate 11 as illustrated in FIG. 4D.
Next, the upper mold 111 and the lower mold 103 are removed and the
filled mold resin 6 is cured. Then, an individualization process
(the dicing process) is performed to individualize the substrates
11 (FIG. 4D).
Here, when the resin for forming the protective layer 3 is dropped
on the substrate 11 so as to cover the entire surface of the
semiconductor lamination portion 21 on the semiconductor chip 2,
the resin has a hemispherical cross section as illustrated in FIG.
4B. That is, the protective layer 3 formed while holding this state
has the thickness increased toward the center.
In the optical device 1 where the protective layer 3 is formed to
have the hemispherical cross section as illustrated in FIG. 1, when
a state where the mold resin 6 is in a dry state and the stress
variation does not occur has changed to a state where the mold
resin 6 is swollen, for example, as illustrated in FIG. 5, the mold
resin 6 expands most at the position of the center of the substrate
11. Therefore, when the protective layer 3 is not disposed, the
center of the substrate 11 significantly curved and the center of
the substrate 11 is depressed. The deformation of the substrate 11
causes variation of the position of the semiconductor lamination
portion 21 formed on the substrate 11, that is, a relative position
of the semiconductor lamination portion 21 to the terminal portion
5. Since the center of the substrate 11 is depressed, the relative
position of the semiconductor lamination portion 21 to the terminal
portion 5 significantly varies as the semiconductor lamination
portion 21 is positioned close to the center of the substrate
11.
Here, the optical device 1 illustrated in FIG. 5 is configured such
that the protective layer 3 is disposed on the substrate 11 so as
to cover the entire surface of the semiconductor lamination portion
21 and the protective layer 3 has the thickness increased toward
the center of the substrate 11.
Therefore, the protective layer 3 acts so as to more reduce the
deformation of the mold resin 6 on the substrate center compared
with the edge portion, thus reducing the deformation of the
substrate 11. Consequently, the amount of variation of the
semiconductor lamination portion 21 is lowered. That is, the
influence on the optical device 1 can be reduced in accordance with
the stress variation of the mold resin 6, thus ensuring the
reduction of variation in property caused by the influence of the
mold resin 6 on the optical device 1.
In the optical device 1, the mold resin 6 includes the through hole
61. Here, in the case where the through hole 61 is disposed, when
the resin forming the protective layer 3 has not expanded, that is,
the resin is in the state of low temperature or dry and similar
state, the protective layer 3 is in the state illustrated in FIG.
6A, for example. On the other hand, when the resin forming the
protective layer 3 has expanded, that is, the resin is in the state
of high temperature or moisture absorption and similar state, the
protective layer 3 is extruded to the through hole 61 side as
illustrated in FIG. 6B. That is, the protective layer 3 becomes to
be housed in the through hole 61 by an increase of the volume due
to the swelling. Therefore, the swollen protective layer 3 also
ensures reducing the stress variation acting on the active portion
12. FIGS. 6A and 6B are exaggeratedly illustrated for facilitating
understanding.
Disposing the through hole 61 ensures reducing the stress caused by
the deformation of the protective layer 3 due to the thermal
history of the optical device 1 to act on the semiconductor
lamination portion 21. This preferably ensures the reduction of the
variation in property of the optical device 1 caused by the
deformation and the like of the protective layer 3, especially in
the optical device 1 that operates in a wide temperature range.
In the case of the optical device 1 illustrated in FIG. 1, the
active portion 12 includes a plurality of the semiconductor
lamination portions 21 electrically connected to one another. This
achieves a high SNR and improves adhesion due to the enlarged
contacted area with the protective layer 3.
While the protective layer 3 is formed mainly for reducing the
variation in the electric property of the optical device 1 caused
by the stress, the protective layer 3 is required not to reduce the
variation in the electric property of the optical device 1 but to
obtain desired variation in the electric property depending on
usage. When the desired variation in the electric property is
required, the protective layer 3 may be formed with desired resin
amount. This preferably ensures controlling a relation between the
resin deformation and the electric property of the optical device 1
in the protective layer formation process.
Next, a second embodiment of the present invention will be
described.
In the second embodiment, in the optical device 1 in the first
embodiment illustrated in FIG. 1, the protective layer 3 is formed
by a spin coat method, and an optical device 1 in the second
embodiment is similar to the optical device 1 in the first
embodiment excluding the difference in shape of the protective
layer 3.
That is, as illustrated in FIG. 7, a protective layer 3a in the
second embodiment has an approximately uniform thickness.
Even in the optical device 1 illustrated in FIG. 7, the protective
layer 3a acts so as to reduce the deformation of the mold resin 6,
similarly to the optical device 1 in the above-described first
embodiment. Since the mold resin 6 includes the through hole 61,
when the resin forming the protective layer 3 has expanded, for
example, the state of high temperature or moisture absorption and
similar state, the protective layer 3a is housed in the through
hole 61. This also ensures the reduction of the deformation of the
mold resin 6, thus reducing the stress variation acting on the
active portion 12. Accordingly, the optical device 1 according to
the second embodiment also provides the operational advantage
equivalent to the optical device 1 in the first embodiment.
Next, a third embodiment of the present invention will be
described.
An optical device 1 in the third embodiment has cavities between a
mold resin and a protective layer.
FIG. 8 is a cross-sectional view illustrating a schematic
configuration of an exemplary optical device 1 according to the
third embodiment of the present invention. For simplification, FIG.
8 illustrates only main parts.
The optical device 1 according to the third embodiment of the
present invention is an optical device where the light receiving
portion or the light emitting portion has a mesa structure, and the
optical device 1 includes a light receiving/emitting element 1100,
a protective layer 1040, a mold resin (a resin sealing body) 1050,
and a terminal portion 1060. As illustrated in FIG. 9, the light
receiving/emitting element 1100 includes a semiconductor substrate
1010, semiconductor lamination portions 1020, electrodes 1031 and
1032, and an insulating coating layer 1033. The optical device 1
illustrated in FIG. 8 receives and emits infrared light via a
surface of the light receiving/emitting element 1100 exposed to a
bottom surface of the mold resin 1050.
The semiconductor substrate 1010 has infrared transparency.
The semiconductor lamination portion 1020 is formed of a first
conductivity-type semiconductor layer (for example, an n-type
semiconductor layer) 1021, an intrinsic semiconductor layer 1022,
and a second conductivity-type semiconductor layer (for example, a
p-type semiconductor layer) 1023, which are laminated on the
semiconductor substrate 1010 in this order. As described below, the
semiconductor lamination portion 1020 can be divided into a mesa
structure portion 1201 formed on the semiconductor substrate 1010
and a bottom portion 1202 as a region excluding the mesa structure
portion 1201 on the semiconductor substrate 1010. The electrodes
1031 and 1032 are formed on at least a part of each of the mesa
structure portion 1201 and the bottom portion 1202,
respectively.
The protective layer 1040 covers the light receiving/emitting
element 1100 (that is, the semiconductor substrate 1010 and the
semiconductor lamination portion 1020). The mold resin 1050
packages the light receiving/emitting element 1100 (the
semiconductor substrate 1010 and the semiconductor lamination
portion 1020) via the protective layer 1040. Furthermore, the mold
resin 1050 includes a through hole 1051 that passes through the
mold resin 1050 to reach a cavity 1041 described below.
The protective layer 1040 has different top surface heights between
on the mesa structure portion 1201 and on the bottom portion 1202
when an interface between the semiconductor substrate 1010 and the
semiconductor lamination portion 1020 is a reference. The cavity
1041 is formed between the protective layer 1040 and the mold resin
1050 at least partially above the mesa structure portion 1201.
The cavity 1041 has a thickness of 2 .mu.m or more and 200 .mu.m or
less, preferably. Difference in linear expansion coefficient
between the protective layer 1040 and the mold resin 1050 is 50 ppm
or more and 500 ppm or less, preferably.
While an illustration is omitted, the light receiving/emitting
element 1100 may be configured such that a plurality of the light
receiving/emitting elements 1100 are connected in series or in
parallel, the electrode 1031 on the mesa structure portion 1201 of
one light receiving/emitting element 1100 is electrically connected
to the electrode 1032 on the bottom portion 1202 of another light
receiving/emitting element 1100 on a part of an inclined surface of
the mesa structure portion 1201 of the one light receiving/emitting
element 1100, and another part of the inclined surface of the mesa
structure portion 1201 of the one light receiving/emitting element
1100 is not covered with a metal.
The following sequentially describes each component.
<Semiconductor Substrate>
In the third embodiment of the present invention, the semiconductor
substrate 1010 is a substrate where the semiconductor lamination
portion 1020 having a photodiode structure of a PN junction or a
PIN junction can be formed. The semiconductor substrate 1010 is not
specifically limited insofar as the semiconductor substrate 1010
has the infrared transparency. The semiconductor substrate 1010 may
be any of a substrate that includes a material including a
semiconductor or an insulating substrate. That is, "the
semiconductor substrate" means a substrate constituting the light
receiving/emitting element 1100 as a semiconductor device. The
semiconductor substrate 1010 includes, for example, a substrate
made of Si, GaAs, sapphire, InP, and similar material. When a layer
including InSb is used for the semiconductor lamination portion
1020, preferably, a GaAs substrate is used from an aspect of
forming the semiconductor lamination portion 1020 with few lattice
defects. In this embodiment, "having the infrared transparency"
means that the infrared transmittance is 10% or more, preferably
50% or more, and more preferably 65% or more.
<Semiconductor Lamination Portion>
The semiconductor lamination portion 1020 in the optical device 1
according to the third embodiment of the present invention has the
photodiode structure of the PIN junction formed of the first
conductivity-type semiconductor layer 1021, the intrinsic
semiconductor layer 1022, and the second conductivity-type
semiconductor layer 1023. The semiconductor lamination portion 1020
in the third embodiment of the present invention is not
specifically limited insofar as the semiconductor lamination
portion has the photodiode structure or an LED structure of the PN
junction or the PIN junction. While the semiconductor lamination
portion 1020 according to the third embodiment has the photodiode
structure of the PIN junction formed of the first conductivity-type
semiconductor layer 1021, the intrinsic semiconductor layer 1022,
and the second conductivity-type semiconductor layer 1023, the
semiconductor lamination portion 1020 may has the photodiode
structure of the PN junction formed of the first conductivity-type
semiconductor layer 1021 and the second conductivity-type
semiconductor layer 1023. A known material that has sensitivity to
infrared may be employed as the semiconductor lamination portion
1020, and for example, a semiconductor layer including InSb may be
employed.
The semiconductor lamination portion 1020 in the optical device 1
according to the third embodiment of the present invention is
divided into the mesa structure portion 1201 and the bottom portion
1202. The mesa structure portion 1201 is indicated by a part raised
in a plateau shape, and the bottom portion 1202 is indicated by the
other part. In this embodiment, the mesa structure portion 1201 is
formed of a part of the first conductivity-type semiconductor layer
1021, the intrinsic semiconductor layer 1022, and the second
conductivity-type semiconductor layer 1023. The other part of the
first conductivity-type semiconductor layer 1021 forms the bottom
portion 1202.
The mesa structure portion 1201 and the bottom portion 1202 are
formed by photolithography and etching. As a method for etching,
wet etching and dry etching may be employed.
<Electrode>
The optical device 1 according to the third embodiment of the
present invention includes electrodes 1031 and 1032 on a top of the
mesa structure portion 1201 and a part of the bottom portion 1202
of the semiconductor lamination portion 1020. The materials of the
electrodes 1031 and 1032 are not specifically limited insofar as
the materials are electrically contactable with the semiconductor
lamination portion 1020. When a plurality of elements in the
optical device are connected in series, it is only necessary that
the electrodes are configured such that the electrode on the bottom
portion 1202 of one element in the optical device is connected to
the electrode on the top of the mesa structure portion 1201 of the
other element. A part of the infrared entered from the substrate
side is reflected by the electrodes 1031 and 1032. Therefore, the
semiconductor lamination portion 1020 covered with the electrodes
having large areas provides an advantage of enhancing the
light-receiving efficiency.
<Insulating Coating Layer>
The optical device 1 according to the third embodiment of the
present invention includes a region not covered with the electrodes
1031 and 1032 and the insulating coating layer 1033 that covers a
part of the semiconductor substrate 1010 on the semiconductor
lamination portion 1020. The optical device 1 according to the
third embodiment of the present invention is not required to
include the insulating coating layer 1033. It is expected that the
insulating coating layer 1033 reduces physical and chemical damages
on the semiconductor lamination portion 1020. A material that has
insulation property and can reduce the physical and chemical
damages may be employed as the insulating coating layer 1033, and
for example, SiO.sub.2, SiN, and a laminated body of them may be
employed. Typically, the insulating coating layer 1033 does not
reflect but mostly transmits the entered infrared.
<Terminal Portion>
The terminal portion 1060 has an electrical connection function and
a role as a supporting portion in assembly. Therefore, the terminal
portion 1060 is disposed to have a top surface and a bottom surface
exposed to top and bottom surfaces of the optical device 1,
respectively.
The electrical connection here means an electrical connection of
the light receiving/emitting element 1100 to an external circuit.
For the electrical connection inside the optical device 1, a wire
1070 disposed by a wire bonding process is used. The wire 1070 is
connected to the terminal portion 1060 and the electrodes 1031 and
1032 of the light receiving/emitting element 1100.
The terminal portion 1060 has a stepped surface 1060a formed by
removing a part of a side facing the light receiving/emitting
element 1100. The wire 1070, made of a conductive material such as
gold (Au), is connected to the stepped surface 1060a of the
terminal portion 1060. The stepped surface 1060a is formed by half
etching of the terminal portion 1060.
The terminal portion 1060 has a thickness of, for example, 0.5 mm
or less.
The terminal portion 1060 is made of a metallic material such as
copper (Cu) or a copper alloy, and iron (Fe) or an alloy containing
iron, and especially, preferred to be made of copper. On the
terminal portion 1060, for example, a nickel (Ni)-palladium
(Pd)-gold (Au) plating may be applied over surfaces other than the
outer surfaces of the terminal portion 1060 exposed from the mold
resin 1050. The nickel (Ni)-palladium (Pd)-gold (Au) plating is a
laminated plating where a nickel (Ni) plating, a palladium (Pd)
plating, and a gold (Au) plating are formed in this order on a
predetermined surface of the terminal portion 1060 made of copper
(Cu) and similar material. The nickel (Ni) plating contributes to
improvement of strength of the terminal portion 1060, the palladium
(Pd) plating contributes to improvement of wire bonding property of
the wire 1070, and the gold (Au) plating contributes to improvement
of solder wettability on mounting. On the terminal portion 1060, an
argentum (Ag) plating may be applied over a surface where the wire
1070 is wire-bonded, and a tin (Sn) plating may be applied over a
top surface (a mounting surface) of the terminal portion 1060
exposed from a top surface of the mold resin 1050. The argentum
(Ag) plating contributes to the improvement of the wire bonding
property of the wire 1070, and the tin (Sn) plating contributes to
the improvement of the solder wettability on mounting.
<Protective Layer>
The optical device 1 according to the third embodiment of the
present invention includes the protective layer 1040 configured to
cover the light receiving/emitting element 1100. The protective
layer 1040 has the top surface height above the mesa structure
portion 1201 lower than the top surface height above the bottom
portion 1202 having the interface between the semiconductor
substrate 1010 and the semiconductor lamination portion 1020 as a
reference. Then, the cavity 1041 is formed between the mold resin
1050 formed on the protective layer 1040 and the protective layer
1040.
The protective layer 1040 may include, for example, photosensitive
silicone. From the aspect of easily forming the cavity 1041, a
material having high water repellency on a surface is preferable.
From the aspect of easily forming the cavity 1041, a material
having high smoothness and good followability to unevenness is
preferable.
The thickness of the protective layer 1040 is not specifically
limited. From the aspect of process margin between the light
receiving/emitting element 1100 protection and the protective layer
1040, the protective layer 1040 is preferred to have the thickness
of 1 .mu.m or more and 200 .mu.m or less from the uppermost portion
of the mesa structure portion 1201.
<Mold Resin>
The optical device 1 according to the third embodiment of the
present invention includes the mold resin 1050 that seals the light
receiving/emitting element 1100 via the protective layer 1040. In
the optical device 1 according to the third embodiment of the
present invention, the light receiving/emitting element 1100 is
sealed by the mold resin 1050 excluding the bottom surface in FIG.
8. However, the mold resin 1050 only needs to be configured such
that the infrared can enter the semiconductor lamination portion
1020 via the semiconductor substrate 1010, and it is not
specifically limited which surface of the light receiving/emitting
element 1100 is covered. For example, the mold resin 1050 may cover
a part of the bottom surface of the light receiving/emitting
element 1100, and does not have to cover a part of the side surface
of the light receiving/emitting element 1100.
A known material including epoxy resin may be employed as the mold
resin 1050, while the material is not limited to this. From the
aspect of generating the cavity 1041, the difference in linear
expansion coefficient between the mold resin 1050 and the
protective layer 1040 is preferably 50 ppm or more, more preferably
100 ppm or more, and further preferably 150 ppm or more. From the
aspect of the process margin, the difference in linear expansion
coefficient between the mold resin 1050 and the protective layer
1040 is preferably 500 ppm or less, more preferably 400 ppm or
less, and further preferably 300 ppm or less.
The mold resin 1050 has a thickness, that is, a length between the
top surface and the bottom surface of the mold resin 1050 in FIG. 8
of, for example, 0.5 mm or less.
The material constituting the mold resin 1050 may include a filler,
inevitably mixed impurities, and similar material besides the resin
material such as the epoxy resin. A mixing amount of the filler is
preferably 50 volume % or more and 99 volume % or less, more
preferably 70 volume % or more and 99 volume % or less, and further
preferably 85 volume % or more and 99 volume % or less among the
materials constituting the mold resin 1050.
The mold resin 1050 includes the through hole 1051 that passes
through the mold resin 1050 to reach the cavity 1041, and the
through hole 1051 only needs to be a through hole extending
perpendicular to the semiconductor substrate 1010 or extending in a
direction close to perpendicular.
Disposing the through hole 1051 in such way ensures the reduction
of the stress in a package due to a thermal history of the optical
device 1.
The through hole 1051 may be disposed on any portion of the mold
resin 1050 insofar as the through hole 1051 penetrates to the
protective layer 1040. For example, the through hole 1051 may be
disposed on a region not overlapping with the cavity 1041. From the
aspect of efficiently reducing the stress, the through hole 1051 is
preferred to be disposed at a proximity of the center of the
protective layer 1040 in top view. A plurality of the through holes
1051 may be disposed, and it is only necessary that at least one
through hole 1051 is disposed.
For example, in a case of the optical device 1 where a plurality of
the mesa structure portions 1201 are arranged in a matrix, the
through hole 1051 may be formed at an upper proximity of the mesa
structure portion 1201 positioned on the center or a proximity of
the center.
The through hole 1051 may be formed in any shape in top view, and
may be formed in, for example, a circular shape and a slit shape.
The through hole 1051 that has the circular shape in top view is
preferable because the through hole 1051 is easily formed with a
high aspect ratio such as "1:100". When it is necessary to prevent
invasion of dust and the like through the through hole 1051 and
similar case, the through hole 1051 is preferred to be formed in
the slit shape.
<Cavity>
The cavity 1041 disposed between the protective layer 1040 and the
mold resin 1050 is formed in a process for forming the protective
layer 1040 and a process for forming the mold resin 1050.
<Method for Controlling Cavity Shape>
The cavity 1041 has a shape (height) that depends on (1) adhesion
of the resin forming the protective layer 1040 with the resin
forming the mold resin 1050, and depends on (2) the difference in
linear expansion coefficient between the mold resin 1050 and the
protective layer 1040. Therefore, adjusting parameters of (1) and
(2) ensures adjusting the shape such as the height and the area of
the cavity 1041 to be formed.
(1) The adhesion of the resin forming the protective layer 1040
with the resin forming the mold resin 1050 can be controlled by
cure conditions of both resins. The adhesion can be controlled also
by a surface treatment process (for example, an oxygen plasma
treatment by RIE (Reactive Ion Etching)) after forming the
protective layer 1040. Therefore, by adjusting the cure conditions
of the resin forming the protective layer 1040 and the resin
forming the mold resin 1050 or process contents in the surface
treatment process after forming the protective layer 1040, the
height of the cavity 1041 can be adjusted.
(2) Depending on the difference in linear expansion coefficient
between the mold resin 1050 and the protective layer 1040, the size
of the cavity 1041 to be formed differs. In a cooling process after
a transfer molding process in a packaging process, the cavity is
allowed to be generated. Then, in this case, as the difference in
linear expansion coefficient is increased, the cavity can be
increased in size, width, and height.
From the aspect of reducing the influence of the stress of the mold
resin 1050, the cavity 1041 has the thickness of, preferably, 2
.mu.m or more and 200 .mu.m or less from the uppermost portion of
the mesa structure portion 1201.
Disposing the cavity 1041 above the mesa structure portion 1201 in
such way ensures reducing the stress variation generated on the
mold resin 1050 to be transmitted to the light receiving/emitting
element 1100 because of the cavity 1041 that serves as a buffer
even when the stress variation is generated due to the expansion of
the mold resin 1050 with heat and similar condition. Therefore, the
stress variation of the mold resin 1050 ensures reducing the
variation of input characteristics or output characteristics of the
light receiving/emitting element 1100, and consequently, reducing
the variation of properties of the optical device caused by the
stress variation of the mold resin 1050.
The cavity 1041 disposed above the mesa structure portion 1201 can
reduce the stress especially acting from above the mesa structure
portion 1201 to the mesa structure portion 1201 and the
semiconductor substrate 1010. In association with the stress
variation of the mold resin 1050, the stress variation is
transmitted from every direction to every direction such as the
mold resin 1050 side and the semiconductor substrate 1010 side.
However, since the cavity 1041 can reduce the stress from every
direction, not only the influence on the light receiving/emitting
element 1100 but also the influence on each portion of the optical
device 1 can be reduced.
<Method for Controlling Cavity Position>
The cavity 1041 can be formed only on a desired position with
higher accuracy by (1) selectively roughening the protective layer
1040 and (2) selectively covering the protective layer 1040 with a
film having good adhesion with the mold resin 1050. Specifically,
before forming the mold resin 1050, the surface of the protective
layer 1040 is roughened or covered with the film having the good
adhesion with the mold resin 1050 excluding a part (a part of the
surface positioned at an upper side of the mesa structure portion
1201) to form the cavity 1041. On the roughened part or the part
covered with the film having the good adhesion with the mold resin
1050 on the surface of the protective layer 1040, the adhesion of
the protective layer 1040 with the mold resin 1050 improves, thus
reducing the generation of the cavity 1041.
(1) In the method where the protective layer 1040 is selectively
roughened, first, as illustrated in FIG. 10A, on the semiconductor
substrate 1010, the first conductivity-type semiconductor layer
1021, the intrinsic semiconductor layer 1022, and the second
conductivity-type semiconductor layer 1023 are laminated in this
order, thus forming the semiconductor lamination portion 1020. In
FIG. 10A, the semiconductor lamination portion 1020 is formed to
have the photodiode structure of the PIN junction formed of the
first conductivity-type semiconductor layer 1021, the intrinsic
semiconductor layer 1022, and the second conductivity-type
semiconductor layer 1023.
Next, the etching is partially performed on the semiconductor
lamination portion 1020, thus forming the mesa structure portion
1201 and the bottom portion 1202 (FIG. 10B). In FIG. 10B, a resist
1024 is partially formed on the semiconductor lamination portion
1020, the wet etching is performed on the semiconductor lamination
portion 1020 where the resist 1024 is partially disposed, thus
forming the mesa structure portion 1201 on the semiconductor
lamination portion 1020. Then, through the processes of element
isolation by ion milling, forming a contact hole, and forming an
electrode pattern, the light receiving/emitting element 1100 is
formed.
Next, the protective layer 1040 is formed on the light
receiving/emitting element 1100 (FIG. 10C). The process for forming
the protective layer 1040 may be appropriately executed
corresponding to the material used for the protective layer. For
example, when a photosensitive protective layer is used as the
protective layer 1040, a rotary coater is used for applying the
protective layer over the light receiving/emitting element 1100,
and baking is performed. After that, exposure is performed with
g-line or i-line of a mercury lamp, developing is performed,
patterning is performed, and subsequently, heating process is
performed to cure. The protective layer 1040 configured to have an
appropriate film thickness ensures generating a desired cavity due
to the effect of the stress. Therefore, the appropriate film
thickness is selected at the portion of the mesa structure portion
1201 so as to preferentially generate the cavity.
Next, a resist 1040a is partially formed on the protective layer
1040 (FIG. 10D). At this time, the resist 1040a is formed only on
the region above the mesa structure portion 1201 and not formed on
the region above the bottom portion 1202.
The resist 1040a may be formed by using a common semiconductor
processing similarly to the case of forming the resist 1024. As the
resist 1040a, metal or resin may be employed.
Then, the region where the resist 1040a is not formed, that is, the
region (the region above the bottom portion 1202) excluding the
region above the mesa structure portion 1201 is roughened. For
example, O.sub.2 plasma RIE is performed for roughening.
Next, after removing the resist 1040a, the wafer after roughening
is individualized into chips by dicing, thus obtaining the light
receiving/emitting element 1100 that includes the protective layer
1040 where a part of the surface is roughened.
Subsequently, on an adhesive tape (not illustrated), a lead frame
(not illustrated) that has an opening and later formed as the
terminal portions 1060, and the light receiving/emitting element
1100 are placed such that the light receiving/emitting element 1100
is positioned on the center of the opening of the lead frame. Then,
for example, the Au wire 1070 is bonded so as to connect the
electrode 1031 of the light receiving/emitting element 1100 to the
lead frame and connect the electrode 1032 of the light
receiving/emitting element 1100 to the lead frame. Finally, the
adhesive tape where the respective components are laminated is
placed on a lower mold (not illustrated) that has a depressed
portion whose thickness is identical to a sum of thicknesses of an
adhesive sheet and the lead frame, and an upper mold (not
illustrated) is pressed against the lower mold with a desired
pressure. The molten resin is poured into the space between the
lower mold and the upper mold and cooled, thus forming the mold
resin 1050. It is only necessary that the curing of the mold resin
1050 is performed at a temperature higher than a temperature of any
glass transition point of the material of the protective layer 1040
and the material of the mold resin 1050, and preferably, the mold
resin 1050 is returned into a room temperature immediately after
termination of heating because cooling proceeds the generation of
the cavity 1041 due to the stress.
Here, in the roughened region above the bottom portion 1202, since
the adhesion of the mold resin 1050 with the protective layer 1040
improves, the cavity 1041 is less likely to be generated.
Consequently, the cavity 1041 is formed only in the not roughened
region above the mesa structure portion 1201.
Then, at this time, a mold that includes a protrusion for forming
the through hole 1051 on a position facing the cavity 1041 is used
as the upper mold as described with FIG. 4C in the first
embodiment, a sheet made of, for example, Teflon (registered
trademark) is disposed so as to cover the entire surface on the
side where the protrusion is formed, and this upper mold is used to
fill the molten resin.
Accordingly, as illustrated in FIG. 10E, the through hole 1051
communicated with the cavity 1041 is formed on the position facing
the cavity 1041 of the mold resin 1050.
Next, the mold resin 1050 is extracted from the lower mold and the
upper mold, and a dicing tape (not illustrated) is laminated on the
surface after removing the adhesive tape. Finally, a dicing blade
is used for cutting the lead frame portion from the surface on the
opposite side of the surface where the dicing tape is laminated.
Then, the individualized optical device (the optical device
illustrated in FIG. 8) is obtained.
(2) In the method where the protective layer 1040 is selectively
covered with the film having the good adhesion with the mold resin
1050, the light receiving/emitting element 1100 that includes the
protective layer 1040 is formed with the procedure similar to the
above description (FIGS. 11A to 11C).
Next, the protective layer 1040 is selectively covered with an
adhesive film 1040b, such as polyimide resin, having the good
adhesion with the mold resin 1050 (FIG. 11D). At this time, the
adhesive film 1040b is formed only on the region above the bottom
portion 1202 and not formed on the region above the mesa structure
portion 1201.
Then, with the procedure similar to the above description, the
upper mold that includes the protrusion for forming the through
hole 1051 communicated with the cavity 1041 on the position facing
the cavity 1041 is used, and the upper mold where the sheet made
of, for example, Teflon (registered trademark) is disposed so as to
cover the entire surface on the side where the protrusion is formed
is used to fill the molten resin, thus sealing the light
receiving/emitting element 1100 by the mold resin 1050 via the
protective layer 1040 (FIG. 11E).
Here, in the region, where the adhesive film 1040b is formed, above
the bottom portion 1202, the adhesion of the adhesive film 1040b
with the mold resin 1050 improves. On the other hand, in the
region, where the adhesive film 1040b is not formed, above the mesa
structure portion 1201, since the adhesion of the adhesive film
1040b with the mold resin 1050 is low, the cavity 1041 is easily
generated. Consequently, the cavity 1041 is formed only above the
mesa structure portion 1201. Furthermore, since the upper mold
includes the protrusion for forming the through hole 1051, the
through hole 1051 communicated with the cavity 1041 is formed on
the position facing the cavity 1041.
The method that selectively roughens the protective layer 1040 may
be combined with the method that selectively covers the protective
layer 1040 with the film having the good adhesion such that, by
roughening only the region where the cavity 1041 is formed on the
protective layer 1040 and disposing the adhesive film 1040b only on
the region where the cavity 1041 is not formed on the protective
layer 1040, the adhesion of the protective layer 1040 with the mold
resin 1050 is improved via the adhesive film 1040b and the adhesion
of the protective layer 1040 with the adhesive film 1040b is also
improved.
<Modification>
In the above-described third embodiment, as illustrated in FIG. 8,
one cavity 1041 may be partially formed above the mesa structure
portion 1201 for each mesa structure portion 1201, while a
plurality of the cavities 1041 may be formed for one mesa structure
portion 1201.
The cavity 1041 is not necessarily required to be disposed for
every mesa structure portion 1201, and the cavity 1041 may be
disposed for only any one of or a plurality of the mesa structure
portions 1201.
In FIG. 8, one cavity 1041 or a plurality of the cavities 1041 may
be disposed not only above the mesa structure portion 1201 but also
partially above the bottom portion 1202. As illustrated in FIG. 12,
the cavity 1041 may be disposed only above the bottom portion 1202.
In this case, the cavity 1041 has the thickness of 2 .mu.m or more
and 200 .mu.m or less. That is, the cavity 1041 may be disposed on
any region between the protective layer 1040 and the mold resin
1050.
As illustrated in FIG. 13, the cavity 1041 may be formed so as to
be overlapped with the entire surface (that is, the whole region
between the protective layer 1040 and the mold resin 1050) of the
protective layer 1040 in top view. In the case where a plurality of
the light receiving/emitting elements 1100 are connected in series
or in parallel and similar case, the protective layer 1040 may be
formed so as to cover the whole of the plurality of the light
receiving/emitting elements 1100 or cover the entire light
receiving/emitting element 1100, thus forming the cavity 1041 over
the entire protective layer 1040. In this case again, from the
aspect of reducing the influence of the stress of the mold resin
1050, the cavity 1041 is preferred to have the thickness of 2 .mu.m
or more and 200 .mu.m or less from the uppermost portion of the
mesa structure portion 1201.
Thus, the cavity 1041 formed over the entire protective layer 1040
ensures more reducing the influence of the stress variation of the
mold resin 1050.
Furthermore, as illustrated in FIG. 14, the protective layer 1040
and the cavity 1041 may be formed to have the hemispherical
surfaces. That is, for example, a potting method may be used for
dropping the protective layer 1040 to form the protective layer
1040 that has the hemispherical surface, and on this protective
layer 1040, the mold resin 1050 is formed so as to form the cavity
1041 having the hemispherical surface. In this case again, the
operational advantage equivalent to the above description can be
obtained.
In this case again, from the aspect of reducing the influence of
the stress of the mold resin 1050, the cavity 1041 is preferred to
have the thickness of 2 .mu.m or more and 200 .mu.m or less from
the uppermost portion of the mesa structure portion 1201. In this
case, the uppermost portion of the light receiving/emitting element
1100 predicted to be arranged on a position closest to the edge
portion of the hemispherical protective layer 1040 may be defined
as the uppermost portion of the mesa structure portion 1201.
Then, the through hole 1051, which passes through the mold resin
1050 to reach the cavity 1041, only needs to be disposed for each
cavity 1041 disposed on each position illustrated in FIGS. 12 to
14.
For simplification, FIGS. 12 to 14 illustrate only main parts.
Thus, even the cavity 1041 that has a different shape or is
disposed on a different location can provide the operational
advantage equivalent to the third embodiment.
In the above-described first to third embodiments, when the
protective layer is made of the material that can sufficiently
reduce the influence of the stress variation caused by the
deformation of the mold resin, the through hole may be disposed on
any position of the mold resin. For example, the through hole may
be disposed on a region overlapped with the protective layer in top
view, may be disposed on a region not overlapped with the
protective layer in top view, or may be disposed on a region not
overlapped with the substrate.
Next, a fourth embodiment of the present invention will be
described.
An optical device 1 according to the fourth embodiment is an
exemplary optical device where a protective layer is made of a
material that can sufficiently reduce the influence of the stress
variation caused by the deformation of the mold resin.
As illustrated in FIG. 15, the optical device 1 according to the
fourth embodiment includes the mold resin 6 without the through
hole 61 in the optical device 1 of the first embodiment illustrated
in FIG. 1. The optical device 1 according to the fourth embodiment
is similar to the optical device 1 in the first embodiment
excluding that the through hole 61 is not formed on the mold resin
6. Then, like reference numerals designate corresponding or
identical elements, and therefore such elements will not be further
elaborated here.
That is, as illustrated in FIG. 15, the optical device 1 according
to the fourth embodiment includes the light receiving/emitting
element 2 that has the photoelectric conversion function, the
protective layer 3, and the terminal portion 5 connected to the
light receiving/emitting element 2 by the wire 4 connected to the
wire pad (not illustrated) of the light receiving/emitting element
2. The light receiving/emitting element 2 includes the substrate 11
and the active portion 12 formed on the substrate 11. The
protective layer 3 is continuously formed to cover the active
portion 12 and to cover at least a part of the substrate 11. The
protective layer 3 is formed to have a thickness increasing toward
the center of the substrate 11. The mold resin 6 is gaplessly
filled on the whole between the terminal portion 5 and the light
receiving/emitting element 2.
The protective layer 3 only needs to be disposed to cover at least
entire surface of the active portion 12, and is not necessarily
required to cover the substrate 11.
A method for manufacturing the optical device 1 in the fourth
embodiment will be described by referring to cross-sectional views
illustrated in FIGS. 16A to 16D.
First, the wafer dicing process is performed to individualize the
substrate 11 from a state of a wafer into chips of the light
receiving/emitting element 2.
Next, a plurality of the individualized semiconductor chips 2 are
fixed on the adhesive sheet 102 where the lead frames 101, which
are formed as the terminal portions 5 later, are fixed, and the
wire bonding process is performed to electrically connect the
semiconductor chip 2 to the terminal portion 5 by the wire 4 (FIG.
16A). The adhesive sheet 102 may be preliminarily included on the
lead frame 101.
Next, a potting process is performed to form the protective layer 3
(FIG. 16B). That is, a resin for forming the protective layer 3 is
dropped on the substrate 11 so as to cover the entire surface of
the active portion 12 of the semiconductor chip 2. Then, a shape of
the dropped resin is held as it is to form the protective layer 3.
This forms the protective layer 3 having the thickness increased
toward the center of the substrate 11. In the resin potting
process, a dispenser device for liquid resin may be used.
Next, the transfer molding is performed by using an upper mold 104,
where protrusions are not formed on a surface facing a lower mold
103, to form the mold resin (FIG. 16C). That is, the upper mold 104
is positioned to contact the terminal portion 5 so as to face the
lower mold 103, and the molten resin is filled between the upper
mold 104 and the adhesive sheet 102 from a side. Before the process
performing the transfer molding, a process to cure the protective
layer 3 may be provided.
Next, the upper mold 104 and the lower mold 103 are removed and the
filled mold resin 6 is cured. Then, an individualization process
(the dicing process) is performed to individualize the substrates
11 (FIG. 16D).
Here, when the resin for forming the protective layer 3 is dropped
on the substrate 11 so as to cover the entire surface of the
semiconductor lamination portion 21 on the semiconductor chip 2,
the resin has a hemispherical cross section as illustrated in FIG.
16B. That is, the protective layer 3 formed while holding this
state has the thickness increased toward the center.
In the optical device 1 where the protective layer 3 is formed to
have the hemispherical cross section as illustrated in FIG. 1, when
a state where the mold resin 6 is in a dry state and the stress
variation does not occur has changed to a state where the mold
resin 6 is swollen, for example, as illustrated in FIG. 17, the
mold resin 6 expands most at the position of the center of the
substrate 11. Therefore, when the protective layer 3 is not
disposed, the center of the substrate 11 is significantly curved
and the center of the substrate 11 is depressed. The deformation of
the substrate 11 causes variation of the position of the
semiconductor lamination portion 21 formed on the substrate 11,
that is, a relative position of the semiconductor lamination
portion 21 to the terminal portion 5. Since the center of the
substrate 11 is depressed, the variation amount of the relative
position of the semiconductor lamination portion 21 to the terminal
portion 5 significantly varies as the semiconductor lamination
portion 21 is positioned close to the center of the substrate
11.
Here, the protective layer 3 is disposed on the substrate 11 so as
to cover the entire surface of the semiconductor lamination portion
21 and the protective layer 3 has the thickness increased toward
the center of the substrate 11.
Therefore, the protective layer 3 acts so as to more reduce the
deformation of the mold resin 6 on the substrate center compared
with the edge portion, thus reducing the deformation of the
substrate 11. Consequently, the amount of variation of the
semiconductor lamination portion 21 is lowered. That is, the
influence on the optical device 1 can be reduced in accordance with
the stress variation of the mold resin 6, thus ensuring the
reduction of variation in property caused by the influence of the
mold resin 6 on the optical device 1.
In the case of the optical device 1 illustrated in FIG. 15,
similarly to the optical device 1 illustrated in FIG. 1, the active
portion 12 includes a plurality of the semiconductor lamination
portions 21 electrically connected to one another. This achieves a
high SNR and improves adhesion due to the enlarged contacted area
with the protective layer 3.
While the above-described protective layer 3 is formed mainly for
reducing the variation in the electric property of the optical
device 1 caused by the stress, the protective layer 3 is required
not to reduce the variation in the electric property of the optical
device 1 but to obtain desired variation in the electric property
depending on usage. When the desired variation in the electric
property is required, the protective layer 3 may be formed with
desired resin amount. This preferably ensures controlling a
relation between the resin deformation and the electric property of
the optical device 1 in the protective layer formation process.
Next, a fifth embodiment of the present invention will be
described.
An optical device 1 according to the fifth embodiment is an
exemplary optical device where a protective layer is made of a
material that can sufficiently reduce the influence of the stress
variation caused by the deformation of the mold resin in the
optical device according to the second embodiment.
As illustrated in FIG. 18, the optical device 1 according to the
fifth embodiment includes the mold resin 6 without the through hole
61 in the optical device 1 of the second embodiment illustrated in
FIG. 7. The optical device 1 according to the fifth embodiment is
similar to the optical device 1 in the second embodiment excluding
that the through hole 61 is not formed on the mold resin 6. In this
case, similarly to the second embodiment, disposing the protective
layer 3 ensures reducing the deformation of the substrate 11 caused
by the stress variation of the mold resin 6, thus ensuring the
reduction of the variation amount of the semiconductor lamination
portion 21, that is, ensuring the reduction of the variation in
property caused on the optical device 1.
Next, a sixth embodiment of the present invention will be
described.
As illustrated in FIGS. 19 and 20, an optical device 1 according to
the sixth embodiment includes the mold resin 1050 without the
through hole 1051 in the optical device 1 of the third embodiment
where the cavity is disposed between the mold resin and the
protective layer illustrated in FIG. 8. The optical device 1
according to the sixth embodiment is similar to the optical device
1 in the third embodiment excluding that the through hole 1051 is
not formed on the mold resin 1050. Then, like reference numerals
designate corresponding or identical elements, and therefore such
elements will not be further elaborated here.
The control method for the shape of the cavity 1041 of the optical
device 1 according to the sixth embodiment is similar to the
optical device 1 in the third embodiment. The control method for
the position of the cavity 1041 is also similar to the optical
device 1 in the third embodiment, while the upper mold used for
forming the mold resin 1050 has a different shape.
That is, in the method (1) where the protective layer 1040 is
selectively roughened, as illustrated in FIGS. 21A to 21E, the
processes similar to the optical device 1 in the third embodiment
are performed from FIGS. 21A to 21D, thus obtaining the light
receiving/emitting element 1100 that includes the protective layer
1040 where apart of the surface is roughened.
Subsequently, on an adhesive tape (not illustrated), a lead frame
(not illustrated) that has an opening and later formed as the
terminal portions 1060, and the light receiving/emitting element
1100 are placed such that the light receiving/emitting element 1100
is positioned on the center of the opening of the lead frame. Then,
for example, the Au wire 1070 is bonded so as to connect the
electrode 1031 of the light receiving/emitting element 1100 to the
lead frame and connect the electrode 1032 of the light
receiving/emitting element 1100 to the lead frame. Finally, the
adhesive tape where the respective components are laminated is
placed on a lower mold (not illustrated) that has a depressed
portion whose thickness is identical to a sum of thicknesses of an
adhesive sheet and the lead frame, and an upper mold (not
illustrated) without the protrusion for forming the through hole is
used to press against the lower mold with a desired pressure. The
molten resin is poured into the space between the lower mold and
the upper mold and cooled, thus forming the mold resin 1050. The
curing of the mold resin 1050 is simply performed at a temperature
higher than a temperature of any glass transition point of the
material of the protective layer 1040 or the material of the mold
resin 1050, and preferably, the mold resin 1050 is returned into a
room temperature immediately after termination of heating because
cooling proceeds the generation of the cavity 1041 due to the
stress.
Here, in the roughened region above the bottom portion 1202, since
the adhesion of the mold resin 1050 with the protective layer 1040
improves, the cavity 1041 is less likely to be generated.
Consequently, the cavity 1041 is formed only in the not roughened
region above the mesa structure portion 1201.
Next, the mold resin 1050 is extracted from the lower mold and the
upper mold, and a dicing tape (not illustrated) is laminated on the
surface after removing the adhesive tape. Finally, a dicing blade
is used for cutting the lead frame portion from the surface on the
opposite side of the surface where the dicing tape is laminated.
Then, the individualized optical device 1 is obtained.
In the sixth embodiment, the protrusion is not formed on the
surface of the upper mold facing the lower mold. Then, as
illustrated in FIG. 21E, the mold resin 1050 does not include the
through hole.
In the method (2) where the protective layer 1040 is selectively
covered with the film having the good adhesion with the mold resin
1050, as illustrated in FIGS. 22A to 22E, the processes similar to
the optical device 1 in the third embodiment are performed from
FIGS. 22A to 22D, thus obtaining the protective layer 1040 covered
with the adhesive film 1040b, such as polyimide resin, having the
good adhesion with the mold resin 1050.
Then, with the procedure similar to the case (1) where the
protective layer 1040 is selectively roughened, the upper mold (not
illustrated) without the protrusion for forming the through hole is
used to seal the light receiving/emitting element 1100 by the mold
resin 1050 via the protective layer 1040 (FIG. 22E).
Here, in the region, where the adhesive film 1040b is formed, above
the bottom portion 1202, the adhesion of the adhesive film 1040b
with the mold resin 1050 improves. On the other hand, in the
region, where the adhesive film 1040b is not formed, above the mesa
structure portion 1201, since the adhesion of the adhesive film
1040b with the mold resin 1050 is low, the cavity 1041 is easily
generated. Consequently, the cavity 1041 is formed only above the
mesa structure portion 1201.
In this case again, the method that selectively roughens the
protective layer 1040 may be combined with the method that
selectively covers the protective layer 1040 with the film having
the good adhesion such that, by roughening only the region where
the cavity 1041 is formed on the protective layer 1040 and
disposing the adhesive film 1040b only on the region where the
cavity 1041 is not formed on the protective layer 1040, the
adhesion of the protective layer 1040 with the mold resin 1050 is
improved via the adhesive film 1040b and the adhesion of the
protective layer 1040 with the adhesive film 1040b is also
improved.
<Modification>
In the above-described sixth embodiment, as illustrated in FIG. 19,
one cavity 1041 may be partially formed above the mesa structure
portion 1201 for each mesa structure portion 1201, while a
plurality of the cavities 1041 may be formed for one mesa structure
portion 1201.
The cavity 1041 is not necessarily required to be disposed for
every mesa structure portion 1201, and the cavity 1041 may be
disposed for only any one of or a plurality of the mesa structure
portions 1201.
In FIG. 19, one cavity 1041 or a plurality of the cavities 1041 may
be disposed not only above the mesa structure portion 1201 but also
partially above the bottom portion 1202. As illustrated in FIG. 23,
the cavity 1041 may be disposed only above the bottom portion 1202.
In this case, the cavity 1041 has the thickness of 2 .mu.m or more
and 200 .mu.m or less. That is, the cavity 1041 may be disposed on
any region between the protective layer 1040 and the mold resin
1050.
As illustrated in FIG. 24, the cavity 1041 may be formed so as to
be overlapped with the entire surface (that is, the whole region
between the protective layer 1040 and the mold resin 1050) of the
protective layer 1040 in top view. In the case where a plurality of
the light receiving/emitting elements 1100 are connected in series
or in parallel and similar case, the protective layer 1040 may be
formed so as to cover the whole of the plurality of the light
receiving/emitting elements 1100, or cover the entire light
receiving/emitting element 1100, thus forming the cavity 1041 over
the entire protective layer 1040. In this case again, from the
aspect of reducing the influence of the stress of the mold resin
1050, the cavity 1041 is preferred to have the thickness of 2 .mu.m
or more and 200 .mu.m or less from the uppermost portion of the
mesa structure portion 1201.
Thus, the cavity 1041 formed over the entire protective layer 1040
ensures more reducing the influence of the stress variation of the
mold resin 1050.
Furthermore, as illustrated in FIG. 25, the protective layer 1040
and the cavity 1041 may be formed to have the hemispherical
surfaces. That is, for example, a potting method may be used for
dropping the protective layer 1040 to form the protective layer
1040 that has the hemispherical surface, and on this protective
layer 1040, the mold resin 1050 is formed so as to form the cavity
1041 having the hemispherical surface. In this case again, the
operational advantage equivalent to the above description can be
obtained.
In this case again, from the aspect of reducing the influence of
the stress of the mold resin 1050, the cavity 1041 is preferred to
have the thickness of 2 .mu.m or more and 200 .mu.m or less from
the uppermost portion of the mesa structure portion 1201. In this
case, the uppermost portion of the light receiving/emitting element
1100 predicted to be arranged on a position closest to the edge
portion of the hemispherical protective layer 1040 may be defined
as the uppermost portion of the mesa structure portion 1201.
For simplification, FIGS. 23 to 25 illustrate only main parts.
Thus, even the cavity 1041 that has a different shape or is
disposed on a different location can provide the operational
advantage equivalent to the sixth embodiment.
While descriptions have been given of the case where the
semiconductor lamination portion has the two-step mesa structure in
the above-described embodiments, the semiconductor lamination
portion is not limited to the mesa structure, and the semiconductor
lamination portion that has any structure may be applied.
WORKING EXAMPLES
The following describes Working Examples of the optical device 1
according to the sixth embodiment of the present invention.
Working Example 1
In Working Example 1, as illustrated in FIG. 24, the cavity 1041
was formed over the entire surface between the mold resin 1050 and
the top surface of the protective layer 1040.
First, the optical device having a PIN diode structure was
manufactured with the following procedure. That is, an MBE method
was employed such that an InSb layer (an n-type semiconductor
layer) where Sn was doped by 1.0.times.10.sup.19 atom/cm.sup.3 was
grown 1.0 .mu.m thick on a semi-insulating GaAs single crystal
semiconductor substrate, an InSb layer (an intrinsic semiconductor
layer) where Zn was doped by 1.times.10.sup.16 atom/cm.sup.3 was
grown 2.0 .mu.m thick on the n-type semiconductor layer, an
Al.sub.0.2In.sub.0.8Sb layer (a barrier layer) where Zn was doped
by 5.times.10.sup.18 atom/cm.sup.3 was grown 0.02 .mu.m thick on
the intrinsic semiconductor layer, and further, an InSb layer (a
p-type semiconductor layer) where Zn was doped by 5.times.10.sup.18
atom/cm.sup.3 was grown 0.5 .mu.m thick on the barrier layer. This
prepared a semiconductor wafer that included the GaAs single
crystal semiconductor substrate 1010 and the semiconductor
lamination portion 1020 having the photodiode structure in the PIN
junction.
A positive photoresist for i-line was applied over a surface of the
semiconductor wafer prepared in such way, and a reduced projection
type exposure device was used for performing exposure using i-line.
Then, development was performed to regularly form a plurality of
resist patterns on the surface of the semiconductor lamination
portion 1020. Then, a hydrochloric acid-hydrogen peroxide solution
was used to perform wet etching, thus forming the mesa structure
portion 1201 and the bottom portion 1202 on the semiconductor
lamination portion 1020.
On the element having the mesa shape, a SiO.sub.2 film was formed
as a hard mask, and subsequently, the element isolation was
performed with ion milling. Then, a SiN film was formed as the
protective layer, and the contact hole was formed by
photolithography and dry etching. Then, the electrodes 1031 and
1032 were formed on the top of the mesa structure portion 1201 and
the bottom portion 1202 respectively by photolithography and
sputtering, thus obtaining the light receiving/emitting element
1100 that included the mesa structure portion 1201 having the area
of 420 .mu.m.sup.2.
A photosensitivity silicone manufactured by Shin-Etsu Astech Co.,
Ltd. was applied over the light receiving/emitting element 1100
manufactured through the above process as the protective layer 1040
using a spin coater at a rotation speed of 1000 rpm. Then, baking
was performed at 120.degree. C. by a hot plate, and the reduced
projection type exposure device was used for performing exposure
using i-line. Subsequently, for accelerating photocrosslinking
reaction, IPA was used to perform development after post baking
which was performed at 120.degree. C. by the hot plate, and
finally, thermal curing was performed to form the protective layer
1040.
The wafer manufactured through the above-described previous process
was individualized into the chips by dicing, the Au wire was
bonded, and the chips were sealed by the epoxy mold resin 1050
manufactured by KYOCERA Chemical Corporation. The mold resin 1050
was cured at the temperature of 175.degree. C. higher than the
temperature of the glass transition point of the resin, and the
mold resin 1050 was returned into a room temperature immediately
after termination of heating.
In the optical device 1 manufactured in such way, the film
thickness of the photosensitive silicone as the protective layer
1040 was measured and found to be 80 .mu.m above the mesa structure
portion 1201. Furthermore, an SEM was used for observing the cross
section of the optical device 1, and it was found that the
protective layer 1040 had the shape corresponding to the unevenness
of the mesa structure portion 1201 and the bottom portion 1202 of
the semiconductor lamination portion 1020. Furthermore, the cavity
1041 having the thickness of 30 .mu.m was observed over the whole
between the protective layer 1040 and the mold resin 1050.
Working Example 2
In Working Example 2, as illustrated in FIG. 23, the cavity 1041
was formed only in the region above the bottom portion 1202, and
the cavity 1041 was not formed in the region above the mesa
structure portion 1201.
In Working Example 2, the thickness of the protective layer 1040
was configured to be 3 .mu.m and the thickness of the cavity 1041
was configured to be approximately 2 .mu.m.
The manufacturing process is similar to Working Example 1 other
than the forming condition of the protective layer (the rotation
speed of the spin coater was configured to be 1000 rpm when the
photosensitive silicone was applied). Then, detail descriptions
will be omitted.
Comparative Example
In Comparative Example, the thickness of the protective layer 1040
was configured to be 3 .mu.m, and the cavity 1041 was not formed.
In Comparative Example, for realizing the structure without the
cavity 1041, a protective layer resin (photosensitive polyimide
manufactured by Asahi Kasei Corporation) having good adhesion with
the mold resin 1050 was selected.
The forming condition of the protective layer 1040 was changed (the
rotation speed of the spin coater was configured to be 3500 rpm
when the photosensitive silicone was applied). Other manufacturing
processes are similar to Working Example 1. Then, detail
descriptions will be omitted.
The following describes the effect of the optical device 1
according to one embodiment of the present invention based on
Working Example 1 and Working Example 2, and Comparative
Example.
First, the optical devices of Working Example 1, Working Example 2,
and Comparative Example were left in an environment of relative
humidity 100% and temperature 25.degree. C. for 24 hours. Next, the
optical devices were moved to an environment of humidity 0% and
temperature 25.degree. C., and resistance inside the light
receiving/emitting element in a process where the optical device
was dried was measured. FIG. 26 shows a resistance variation rate
to a drying elapsed time relative to a resistance value at a
measurement starting time point. In FIG. 26, a characteristic line
L1 indicates Working Example 1, a characteristic line L2 indicates
Working Example 2, and a characteristic line L3 indicates
Comparative Example.
The internal resistance variation rates at 40 hours on the drying
elapsed time were, approximately, 3 to 3.5% in the optical device
of Comparative Example, 0.5% in Working Example 2, and 0.1% in
Working Example 1.
As indicated in FIG. 26, it was found that the relation between the
electric property and the stress (for example, due to the state of
moisture absorption/drying) of the optical device could be
controlled depending on the size of the cavity. A desired
correlation is required depending on usage, and the effects of the
present invention can be provided even on such usage. That is, in
this case, for realizing the desired relation between the electric
property and the stress, the number of the cavities, the position,
and the shape can be controlled by the conditions in the
manufacturing process.
While only the resistances in the optical devices were compared
here, sensitivity of a sensor when the sensor is configured
including the optical device, or an amount of luminescence of a
light emitting device when the light emitting device is configured
including the optical device is similarly influenced by the
moisture absorption and drying, thus providing similar effects.
While the embodiments of the present invention have been described
above, the above-described embodiments merely illustrate devices
and methods for embodying the technical idea of the present
invention, and the technical idea of the present invention does not
specify the materials, the shapes, the structures, the arrangement,
and similar factor of the components. The technical idea of the
present invention can be variously modified within the technical
scope specified in claims described in CLAIMS.
INDUSTRIAL APPLICABILITY
The optical device according to one embodiment of the present
invention having properties of high sensitivity, high luminous
efficiency, low noise, downsized, high reliability is applicable to
a gas sensor, and furthermore, the NDIR gas sensor that employs the
optical device according to one embodiment of the present invention
is applicable to air monitoring.
REFERENCE SIGNS LIST
1 optical device, 2 light receiving/emitting element, 3 protective
layer, 4 wire, 5 terminal portion, 6 mold resin, 11 substrate, 12
active portion, 31, 32 electrode, 61 through hole, 101 lead frame,
102 adhesive sheet, 103 lower mold, 104 upper mold, 111 upper mold,
111a protrusion, 112 sheet, 1010 semiconductor substrate, 1020
semiconductor lamination portion, 1021 first conductivity-type
semiconductor layer, 1022 intrinsic semiconductor layer, 1023
second conductivity-type semiconductor layer, 1024 resist, 1031,
1032 electrode, 1033 insulating coating layer, 1040 protective
layer, 1041 cavity, 1050 mold resin, 1051 through hole, 1100 light
receiving/emitting element, 1201 mesa structure portion, 1202
bottom portion
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